Control of small phase arrays to form a prescribed amplitude-phase distribution

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989.     

An oscillatory system with a magnetic-fluid viscoinertial element

Results of measuring the damping factor of an oscillatory system the viscoinertial element of which is represented by a magnetic fluid filling a U-shaped glass tube are considered. The role of elasticity is played by an air-filled cavity that is formed in one of the tube legs under the piezoelectric plate attached to its end and serving for oscillation reception. A method of measuring the oscillation damping factor is proposed, and the results of these measurements are used to determine the shear viscosity of magnetic fluid samples as a function of magnetic field strength.     

Magnetophoresis of Microparticles in a Magnetic Fluid

Russian Physics Journal - An experimental setup is developed for studying magnetophoresis in a layer of a magnetic fluid several millimeters thick by the method of light transmission and...     

Study of demagnetizing field induced by a sound wave

The dynamic demagnetizing factor N _d used to describe perturbation of magnetization of a magnetic fluid by a sound wave has been studied. Experimental N _d values obtained according to the proposed methodology have been compared with the results of a model theory based on the approximating function for bodies of cylindrical shape and oblate ellipsoids of rotation.     

Free oscillations of magnetic fluid in strong magnetic field

The paper presents the esults of measuring the elastic parameters of an oscillatory system (coefficient of pondermotive elasticity, damping factor, and oscillation frequency) whose viscous inertial element is represented by a magnetic fluid confined in a tube by magnetic levitation in a strong magnetic field. The role of elasticity is played by the pondermotive force acting on thin layers at the upper and lower ends of the fluid column. It is shown that, by measuring the elastic oscillation frequencies of the magnetic fluid column, it is possible to develop a fundamentally new absolute method for determining the saturation magnetization of a magnetic colloid.     

Elasticity of a magnetic fluid in a strong magnetic field

Complex measurements of the following elastic-magnetic parameters of a magnetic fluid suspended by magnetic levitation within a horizontal tube in a strong magnetic field were performed: the oscillation frequency and decay coefficient; the static, ponderomotive, and dynamic elasticity coefficients; the fluid displacement under hydrostatic pressure; magnetization curve; and the magnetic field strength and gradient. Calculations based on a model of ponderomotive elasticity with correction for the resistance of a viscous fluid in motion and on the fluid column displacement for two magnetic fluid samples agree well with the experimental magnetization curve. The discussed technique holds promise for research into magnetophoresis and nanoparticle aggregation in magnetic colloids.     

“Wall Viscosity” of Magnetic Fluid Oscillations in a Strong Magnetic Field

Russian Physics Journal - The authors provide an estimation of the “wall viscosity” and its increment (“magneto-viscous” effect) in a thin near-wall layer of a column of...     

Perturbation of magnetization of a magnetic fluid by ultralow thermal fluctuations accompanying a sound wave

The paper presents the results of theoretical and experimental research of the the effect of perturbation of the magnetization of a magnetic fluid caused by thermal fluctuations in an adiabatic sound wave in the initial area of the magnetization curve. Measurements are conducted on samples of a magnetic colloid with various viscosity of the dispersion medium in the frequency range of 20–60 kHz. In this frequency range, the studied samples are characterized by the absence of thermal relaxation of magnetization. Comparison of the conclusions of the thermal magnetization relaxation model with the results of experiment make it possible to obtain information on the rheological features of the neareast molecular environment of a particle, i.e., nanorheology.